Wave guide coupling device



Nov. 30, 1948. w. E. BRADLEY WAVE GUIDE COUPLING DEVICE Original Filed Aug. 15, 1944 mmvron WILLIAM E. BRADLEY ATTORNEY Patented Nov. 30, 1948 UNITED STATES TENT OFFICE WAVEGUIDE CQUPLING DEVICE Vania Original application August 15, 1944, Serial No. 549,618. Divided and this application August 31', 1944', Serial No. 552,173

8 Claims. 1

This application is a division of my abandoned application Serial No, 549,618, filed August 15, 1944, and relates in. general to the fields of ultrahigh frequency signaltransmission and more particularly concerns novel means for generating particular modes of wave transmission.

In micro-wave transmission in wave guides and in various other applications, it is often desirable to transmit a single oscillation mode. For exampie, for transmission over a considerable distance, it is well known that the TEm mode of propagation is that which involvesv the lowest attenuation loss.

Moreover, for certain. directional antenna structures, it is desirable to excite the antenna with a particular oscillation. mode in order to obtain the required directional characteristic, as for example, a horizontally polarized energy distribution pattern omnidirectional in the horizon-tal plane. An antenna array comprising a plurality of stacked biconical horns upon a slotted cavity resonator gives an excellent horizontal polarization characteristic of high directivity. The antenna structure is simpler and has lower loss than the conventional stacked di-pole array and is better adapted to operation on ultra high frequencies. It therefore has considerable application in micro-wave transmission.

However, in order to obtain a uniform circular energy distribution from the stacked biconical horn antenna, it has been found that excitation must bev accomplished by the TEoi mode of oscillation. Should other modes enter the cavity which feeds the antenna, the field distribution pattern at a distance from the antenna will no longer be quite circular, but. will have, pronounced symmetrical lobes, the number of which will be determined by the nature. of the spurious oscillation modes. For example, it has been found that attempts to excite a TEM oscillation mode have been accompanied by the generation of a considerable TEzl mode in a circular pipe.

Since the TE21 oscillation can exist in a smaller diameter pipe than the 'IEor, it is ordinarily difficult to remove this spurious mode. In the stacked biconical horn antenna structure, the TEzi wave will result in a pronounced four-way symmetry over the circular horizontal field distribution obtained by the T5101 wave alone.

In the past, attempts to generate the low attenuation TEOI oscillation mode have been accomplished by complex driving apparatus and have resulted in an impure wave, including several other oscillation modes. It has thus become the practice to attempt to resonate the antenna structure whenever poss b fo the TEM wave in order that. mammum p w r u put at this mode could be obtained.

My invention contemplates a wave guide transmission system including a number of transducers permitting the excitation in one central cavity of the 'IEm wave in its pure state.

In order to excite the TE01 mode, in a circular wave guide, my invention contemplates the use of a driving network which couples into the. circular wave guide through symmetrically arranged slots, excited to an equal extent in. the same time phase with respect to the circular wave of the TEm mode and in the same sense. Feeding energy into the wave guide through a slot prevents any longitudinal field and thus prevents coupling; to modes having longitudinal field patterns.

For carrying out my invention, the driving net,- work is coupled into the circular guide in four symmetrical quadrants. All four quadrants are excited equally in the same sense and in the same time phase with respect to the circular wave of the TEM mode.

In each quadrant, electrical energy is fed. into the wave guide through a slot. The four slots are equally driven from a symmetrically branch.- il'lg wave guide. The symmetry insures equal excitation and appropriate phasing of each slot.

It is therefore an object of my invention to provide means for generating the T1301 wave. in its pure state.

Another object of my invention is to provide transducers for coupling an oscillating source to a wave guide or the like which will transmit only the TEM oscillation mode.

A further object of my invention is to, provide a means for coupling a rectangular wave guide to a circular Wave guide in such a manner that the transmitted wav-e excited in the circular wave guide is essentially the TE mode.

Another object of my invention is to generate the TEM oscillation mode in pure form in a circular wave guide.

Still another object of my invention is to utilize a novel arrangement. of symmetrical slits in an end plate of a wave guide, resulting in the generation of a pure TEOl wave.

These and other objects of my invention will now become apparent from the following specification taken in connection with the accompanying drawings in which y Figure 1 is a perspective view of a form of wave guide having means" for exciting only the; TEo oscillation mode therein.

Figure 2 is a front view of the end plate utilized for closing the guide illustrated in Figure 1.

Figure 3 is a top view of the cavity driving means illustrated in Figure 1.

Figure lis across-sectional view of the slot driving means'taken along the line 4-4.

Figure 5 is an illustration of the field distribution at slits in a plate.

As previously mentioned, it has long been known that the TEM wave or the H01 wave is that mode of oscillation which undercertain conditions is least attenuated during transmission. On the other hand, this oscillation. mode has been difficult to excite without attendant development of undesirable high attenuation transmission modes. s r

In the parent case, of which this is a division, I have shown a stacked biconical horn array This is more clearly shown in Figure 4 which shows the individual guide sections 14 to 11 opening into the guide section 66 at points such as 61. As is illustrated in this figure, the rectangular guide section 66 is bisected by a'metal partition 69 which extends tothemetal surface 63. The partition 69 in addition to bisecting the guide section 66 separates the four guide sections 74 to "11, covering the rectangular slits ill to 13.

As illustrated in Figure 1, the vertical rectangular wave guide 65 extends beyond the four crossed guide sections 65,,and is directly coupled to the input wave guide 6|. Thus the energy fed over the wave guide- 61 divides equally on both sides of the bisecting plate 69 of wave guide 55. Energy in each half of wave guide 66 in turn divides utilized to develop a field distribution having a zontally polarized signal and has omnidirectional vertical activity.

- This antenna structure which has lower loss and far greater utility due to its simplicity than the usual stacked dipole array is, as stated, de-

pendentfor proper orientation upon the excitation by the TEM in pure form.

Inthe 'following description, various means will be illustrated embodying my invention for generating a TEuiwave. It is to be understood that the application of the: transducers to be described'is not necessarily-limited to the biconical jhorn antenna disclosed, but may be utilized wherever transmission of micro-wave for a considerable distance is required.

In Figures 1 to 4 there is illustrated a transducer for generating the TE01 transmission mode inpure form in a circular wave guide by utilizing a four-way symmetry.

As illustrated in Figure 1, a rectangular wave guide 6! carrying energy from an ultra-high freuuency source is coupled through a transducer to the circular wave guide 62. The transducer or coupling element is constructed with four-way symmetry'so as to permit the excitation of the TEM mode in the circular wave guide 62. An end plate 63 covering the circular wave guide B2fis perforated to provide as illustrated in Figu'r'e'l, four rectangular slots 10 to I3 dividing the circular surface into quadrants as shown.

Securely fitted to the metal'end plate 63 is a transducer section 65 comprising four rectangular wave guide sections M to 11, positioned directly over the corresponding rectangular slots I'll to '13. These rectangular wave guide sections M te H are opened at that point where they contact the slits 10 to 13 and accordingly permit the transfer'of energy from the guide sections to the circular wave guide 62.

jg-The rectangular wave guide sections 14 to H extend radially inward and are coupled to another rectangular wave guide section 66 which as is illustrated in Figures 1,; 3 and 4, is vertically disposed and provided with plate 69 to bisect the four wave guides, two of the wave guides 14 and '15 being on one side and wave guides 16 and (1 being on the opposite side of the plate.

equally between the two wave guide sections 14 and 1'5 fed from one side of the barrier 69, and the two wave guides 16 and Ti fed from the other side of the barrier 69.

As will now be clear, the four wave guides M to Ti terminating in the slots ill to 13 have a fourway symmetry in the circumferential or angular dimension, each quadrant of which produces an equal component of electromotive force in the same time phase and in a circumferential direction so as to be additive in efiect. That is to say, the E. M. F. are in the same sense when passing continuously around the circumference. If there is negligible net longitudinal E. M. R, as is true with slot couplings and ii the wave guide diameter is chosen greater than the cut-off diameter for the TEOI mode but smaller than the next mode which could also be excited by this drive, a TEm mode in pure form will be excited.

This construction howeverkeeps out entirely the TEzi mode. As schemati-callyshown in Figure 5, the wave guide, if excited as shown by the dotted arrows, would have two opposed couplings to the TEZ]. and this mode will therefore fail to be excited.

Energy from the input wave guide BI is thus coupled to the circular guide 62 through the symmetrical four-way drive illustrated in Figures 1 to 4 so that the field in the circular wave guide beyond the end plate 63 is that of the TEM mode alone.

The circular waveguide 62, as already stated, is chosen such that its diameter is greater than that required to transmit the TEM mode. However, this diameter is smaller than that required for transmission of the next higher mode.

If, however, it is desired to transmit this energy in av larger diameter pipe, and accordingly minimize attenuation, a flared fitting as shown in my parent application may be usedas a coupler between wave guide section 62 and a larger diameter circular wave guide. As the TEzi mode is completely suppressed as described, the energy propagated in the larger ,diametersection is essentially the TEM mode in pure form.

While for purposes of illustration I have shown a transducer provided with four slits, it will now be apparent that more than four slits symmetrically arranged may be used in generating the TEOl mode in a circular wave guide- 'My invention thus may take on. other forms and I do not wish to be limited .bythe illustrations herein given but only by the claims hereof.

I claim:

1. In a high frequency, system, a rectan ular wave guide for carrying energy from a high frequency source, a' second wave. guide of circular cross-section and a coupling element. connected on theends' of said wave guide's comprising a pair of coupling rectangular wave guides coupled at one end to said first mentioned wave guide, the energy in said first wave guide dividing equally in each of said pair of Wave guides, and four additional rectangular wave guides, each pair of said additional wave guides being coupled to one of said first mentioned pair of Wave guides, the energy in each of said first mentioned pair of wave guides in turn dividing in each of the wave guides coupled thereto and each of said last mentioned pairs of wave guides being in turn coupled to said circular wave guide, and having a four way symmetry for exciting the TEOl mode in said second wave guide.

2. In a high frequency system, a rectangular Wave guide carrying energy from a high frequency source; a second wave guide of circular cross-section having a plate closing one end thereof, said plate having at least four symmetrically disposed slits therein, means comprising a corresponding number of coupling rectangular wave guides fed from said rectangular wave guide, and extending to said plate, each of said last mentioned wave guides having open ends juxtaposed to the slits in said plate, and a pair of rectangular wave guides, each coupled at one end to said first mentioned rectangular wave guide and at the other end to individual pairs of said coupling Wave guides.

3. In a high frequency system, a rectangular wave guide carrying energy from a high frequency source; a second wave guide of circular cross-section having a plate closing one end thereof, said plate having at least four symmetrically disposed slits therein; means comprising a corresponding number of rectangular Wave guides fed from said rectangular wave guide, extending radially and connected to said plate, each of said radial wave guides having open ends connected to corresponding slits in said plate, and means coupling the opposite ends of rectangular wave guides to said first mentioned wave guides.

4. In a high frequency system, a rectangular wave guide carrying energy from a high frequency source; a second circular wave guide having a flat plate closing one end thereof, said plate having at least four radial slits symmetrically disposed therein and means comprising a corresponding number of wave guides fed from said rectangular wave guide, and extending radially with respect to said second guide to said plate, each of said last mentioned wave guides having open ends juxtaposed to the slits in said plate.

5. In a high frequency system, a rectangular Wave guide carrying energy from a high frequency source; a second circular wave guide having a flat plate closing one end thereof, said plate having at least four rectangular radially and symmetrically disposed slits therein, and

means comprising a corresponding number of wave guides radially disposed with respect to said circular Wave guide and fed from said rectangular Wave guide, and extending to said plate, each of said last mentioned Wave guides having open ends juxtaposed to the slits in said plate.

6. In a high frequency system, a rectangular wave guide carrying energy from a high frequency source; a second circular wave guide having a flat plate closing one end thereof, said plate having at least four rectangular symmetrically disposed slits therein and a transducer comprising four rectangular Wave guides radial with respect to said circular wave guide and fed from said rectangular wave guide at one end and having openings at their opposite ends cooperating with said slits for transferring energy to said circular wave guide.

7. In a. high frequency system, a rectangular wave guide carrying energy from a high frequency source; a second circular wave guide having a plate closing one end thereof, said plate having at least four rectangular symmetrically disposed slits therein, and a transducer comprising four wave guides radially disposed with respect to said circular wave guide and terminating in rectangular openings providing a four way symmetry, said wave guides being fed at one end from said rectangular wave guide, said openings being juxtaposed to said slits in said plate, producing therein equal components of electromotive force in the same time phase and additive for the TEM mode.

8. In a high frequency system, a. rectangular wave guide carrying energy from a high frequency source; a second circular wave guide having a plate closing one end thereof, said plate having at least four rectangular symmetrically disposed slits therein, and a transducer comprising four wave guides terminating in rectangular openings providing a four-way symmetry, said wave guides being fed at one end from said rectangular wave guide, said openings being juxtaposed to said slits in said plate, producing therein equal components of electromotive force in the same time phase and additive for the TEM mode, and balancing out the TE21 mode,

WILLIAM BRADLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,106,768 Southworth Feb. 1, 1938 2,129,669 Bowen Sept. 13, 1938 2,129,714 Southworth Sept. 13, 1938 2,153,728 Southworth Apr. 11, 1939 

